The present invention relates to an arrangement and a method for measuring the rate-of-turn of a ship by means of a rate-of-turn sensor.
A ship has three degrees of rotational freedom, namely roll, pitch and turn. In service, a ship, and therefore a shipborne rate-of-turn sensor, is subjected to all three motions, either independently or simultaneously. The rate-of-turn sensor should primarily respond to turn motions and should be insensitive to roll and pitch motions.
Rate-of-turn sensors, such as the gyro rate sensor or the vibrating wire sensor, are known and respond primarily to motions about one axis. Employing rate-of-turn instrumentation on Very Large Crude Carriers (V.L.C.C.'s) to assist in berthing maneuvers and during manual steering has, however, been found to be impossible as the information displayed was meaningless.
It was then suggested to support a rate-of-turn sensor onboard ship by a stabilized platform, i.e., a platform which is automatically and continuously maintained in a horizontal position, notwithstanding the movements of the structure of the ship, for example the bridge of the ship, so as to measure the Azimuth rate-of-turn.
Notwithstanding the application of such expensive stabilized platform, it was found that the information displayed was still meaningless, for the equipment proved to be sensitive to outputs related to roll and pitch motions of the ship.